<!DOCTYPE html>
<html>
<head>

<style type="text/css">
a:link, a:visited {
  border-style: solid;
  border-width: 5px;
  border-color: transparent;
  }
a:hover {border-color: gray;}
</style>

</head>

<body>

<a href="#">AAA</a>
<a href="#">BBB</a>
<a href="#">CCC</a>

</body>
</html>